If you want to start building bikes I strongly suggest joining the framebuilders list or some of the online forums. There's a heap of things you can do to make your life easier, and having someone you can visit to see how they do stuff will teach you things you don't even think to ask. The Atomic Zombie crew or other garage homebuilders would be perfect if there's a group like that near you. Recumbent homebuilders are often equally useful and will probably help you even if you want to build a wedgie.

The advantage is that you built it yourself, and if you want something unusual you can build it. The disadvantage is that it's an expensive, time-consuming way to get an inferior bike. The first one you build will not be professional quality, you'll be lucky if it works at all. So if you want a traditional diamond frame bike the only reason to build it is because you can (like Suzy did). If you want a weird bike then you might find you have to either pay a professional framebuilder or do it yourself. Unless you already have a metalworking shop, it's cheaper to pay someone, even if they've never done anything like your bike before (so you get a first attempt that kinda works).

The reward is that you get something you built yourself. It's especially fulfilling when someone you approached initially who refused to build it sees your version and turns it into a commercial product (Greenspeed make a tandem that converts to a solo trike now, because I showed them it could be done).

@hhh: to work well on thin tube a TIG welder needs to have pulse and a foot pedal, which normally means a newer, more expensive welder. I paid ~$US2000 on eBay for mine. It's hobby-level but has the controls I need (if I ran it all day every day I expect it would fail after a couple of months). An old, second hand TIG unit probably won't have pulse, but if you can find one that does it could be a really good thing to buy. Can you at least tell us which country you're in (in your profile) so I can make better suggestions?
–
МסžMar 16 '11 at 21:33

I'm not sure how a compressor would be used for vacuum bagging -- what you need is a vacuum pump.
–
Jerry CoffinFeb 19 '11 at 0:29

Yes. But a compressor can be used as a poor manś vacuum pump by hooking a hose to the air intake. Ideally you have a proper vacuum pump but I've never had the budget so it didn't occur to me, sorry.
–
МסžFeb 19 '11 at 22:42